You gotta fix it so you can sell it, right? You're not gonna chuck it? Or is it so cheap that you can total it is best answer? If you can get the parts cheap, fix it, then sell or try the good tubes and see how you feel about it. You'll know what to do at the time. You could contact a tranny winder to see if they can make new trannies for you, but I doubt it would be cheaper than replacement parts from China. You could get some superduper custom output trannies from Bud Purvine or magnequest as an upgrade, but you still need them installed. Maybe a few fuses to protect the transformers would be a good idea too. For all that effort and money to change them, it's a better value to buy something already there.
If you can live with 16W Opera 211, then you can live with VAC Ren 30/30, or Atma-sphere S30, both make 30W. The OTL needs 8ohm minimum, no foolin. My Manley SEPP 300Bs are very sweet, making 22W. All octal front, adjustable feedback, they could handle the 4ohm 90dB Ushers. If you don't need 65W from a pair of 300b in the 7070, then also consider the VAC Ren 3030 makes 30W. These are all <4k when they pop up. The older used VACs have a lot of upgrades available, like tube Sentry and Signature parts upgrades. Same deal with older Atma-Spheres, they are cheap but the current version is noticeably better. These are reliable US brands, you can call and talk to the designer any weekday.
Ask yourself if you are finished with the Opera yet. Listen closely for the answer over a day. Then say OK, what's next? Then look for the perfect opportunity. It will hit you on the head.
